Running out of steam is usually what has kept me from being much of a fiction writer... I have a story idea, I take it and run with it... and then lose interest.
Most of the time, it's because I get sidetracked after a little while and take off on a "side story" after a little while. And then I can never go back an pick up the original trail where I left off.
Some of it is probably because I am really ADHD... hence the "short form" format of Steemit really suits me.